In the circuit board industry, metalized via hole is widely used to connect surface of circuit board and circuit pattern on back side or electronic means or the like, or electrically connects conductor layer between each layer circuit board of double-layer or multi-layer circuit board to each other, so as to implement the design of multi-layer circuit pattern.
In the prior art, methods of manufacturing single-layer circuit board with metalized via hole mainly comprises the following steps: manufacturing copper foil via flattening or electroanalysis; bonding the copper foil on the substrate via high temperature lamination, to form overlaying copper plate; drilling a hole and removing dirt on the overlaying copper plate; forming conductive seed layer on the hole wall via processes of electroless copper (PTH) or black hole, shadow or the like; forming a metal conductor layer on the hole wall via electroplating, to form overlaying copper plate with metalized hole; covering the overlaying copper plate with photoresist film, using lithography machine for exposure and development, then implementing etching to remove copper layer outside of circuit region on the overlaying copper plate, thereby achieving circuit board with circuit pattern.
Additionally, manufacturing methods for multi-layer circuit board with metalized via hole mainly involves stitching, comprising the following steps: manufacturing single-layer circuit board; implementing laying-up plate and lamination in the order of copper foil, PP(prepreg), single-layer circuit board, PP, single-layer circuit board, . . . , PP, copper foil; drilling through hole for the multi-layer plate after lamination and drilling blind hole for upper layer copper foil, and implementing hole metalization; applying pattern electroplating or panel electroplating to uppermost layer and lowermost layer of the copper foil, achieving circuit pattern. Wherein hole metalization is also usually achieved via process of electroless copper or black hole, shadow or the like to form conductive seed layer on the hole wall and then via electroplating or the like to form conductor thickening layer.
In the process of forming single-layer or multi-layer circuit board with metalized hole via above-mentioned methods, if it is desired to drill a hole with diameter of less than 100 μm on the substrate, currently laser drilling technology has to be utilized. At the time, it need to implement thinning in advance to the part of copper foil to be drilled, afterward use laser to drill a hole, then after drilling the hole, implement electroless copper and electroplating. However, in the etching thinning process, once etching position generates deviation, it will result in that drilling position on the substrate also generates deviation. Also, when implementing metalization to mini-hole, binding force between electroplating copper layer and hole wall is weak, copper layer easily peels off from the hole wall. Additionally, the minimal diameter of micro-hole manufactured on the overlaying copper plate utilizing prior art is 20-50 μm, when the diameter is less than 20 μm, it will generate a hole with too high thickness-diameter ratio and problems of hole wall copper layer being nonuniform or the like will occur at the time of electroless copper and electroplating. Within micro-hole region, nonuniform distribution of current density will result in that the deposition rate of copper at micro-hole surface is larger than the deposition rate of hole wall and bottom. Therefore, void or crack easily forms in the deposition process, it will also result in that the copper thickness of hole surface is larger than the copper thickness of hole wall.
Additionally, above-mentioned methods of producing circuit board need to produce finished overlaying copper plate in advance, afterward implementing drilling and hole metalization to the finished overlaying copper plate, then make circuit pattern via procedure of pasting film, exposure and development, etching or the like, thus the process procedure is long, the producing cost is high. Also, because there are several metal etching in the whole process procedure, thus it will generate plenty of waste water containing metal ion, generating significant harm to environment.